X-ray fluoroscopic apparatus

Abstract

An X-ray fluoroscopic apparatus comprises an X-ray tube for emitting X-rays to an object to be examined, an image intensifier for converting an X-ray image of the object to an optical image, a TV camera for picking up the optical image through a light-tight optical system coupled to the output portion of the image intensifier, an A/D converter for converting an output analog signal of the TV camera to a digital image signal, a selector for outputting the output of the A/D converter to its first and second outputs, an offset memory connected to the first output terminal of the selector, a subtracter for subtracting the output of the offset memory from the second output terminal of the selector, and an image memory to which the output of the subtracter is supplied. When no X-rays are emitted, the selector is connected to the side of the first terminal and an offset signal for each of pixels for one frame output from the TV camera is written into the offset memory. When X-rays are emitted, the selector is connected to the side of the second terminal and the output of the offset memory is subtracted from the X-ray image signal by the subtracter so that an offset-compensated image signal for each of pixels is stored in the image memory.

What is claimed is: 
     
       1. An X-ray fluoroscopic apparatus comprising: means for emitting X-rays toward an object to be examined;   means for converting X-rays transmitted through the object into an optical image;   means for receiving the optical image, coupled to an output portion of said converting means to allow only light from said converting means to reach said receiving means;   means for storing one frame of offset signals that correspond to one frame of output from said receiving means when said receiving means does not receive an optical image from said converting means; and   means for subtracting each of the offset signals stored in said storing means from a corresponding image signal from said receiving means, said receiving means producing a plurality of image signals to form one frame when the optical image is received from said converting means.   
     
     
       2. The apparatus according to claim 1, wherein said converting means includes an image intensifier; said receiving means includes a solid-state image pickup device having an array of light receiving elements in a two-dimensional array;   said storing means stores an offset signal for each of said light receiving elements of said solid-stat image pickup device; and   said subtracting means subtracts the offset signal for each of said light receiving elements from the output of each of said light receiving elements of said solid-state image pickup device.   
     
     
       3. The apparatus according to claim 2, wherein said storing means includes means for sequentially storing the most recent frame of offset signals output from said receiving means. 
     
     
       4. The apparatus according to claim 3, wherein said storing means includes a selector and an offset signal memory coupled to a first output terminal of said selector, said selector connecting said frame memory to said receiving means when X-rays are not emitted from said means for emitting X-rays, and said subtracting means includes a subtracter connected between a second output terminal of said selector and said offset signal memory, said selector connecting said subtracter to said receiving means when X-rays are emitted from said means for emitting X-rays.   
     
     
       5. The apparatus according to claim 2, wherein said storing means includes means for calculating a plurality of average values, each average value based on a plurality of offset signals for each of said light receiving elements over a predetermined number of frames, and average value storing means for storing said plurality of calculated average values over the most recent predetermined number of frames. 
     
     
       6. The apparatus according to claim 5, wherein said storing means further includes a selector connected to the output of said receiving means, said calculating means includes a frame averaging circuit, connected to a first output terminal of said selector, which outputs the average value during the next predetermined number of frames, and   said average value storing means includes a first and a second offset signal memories, both connected to an output of said frame averaging circuit, said first and second offset signal memories alternately receiving average values from said frame averaging circuit, and   said subtracting means includes a subtracter connected to a second output terminal of said selector and said first and second offset signal memories for subtracting the output of the offset signal memory that is not currently receiving average values from said frame averaging circuit from the output of said selector.   
     
     
       7. The apparatus according to claim 1, wherein said receiving means includes a solid-state image pickup device having an array of light receiving elements in a two-dimensional array, vertical transfer CCDs for said light receiving elements, and a horizontal transfer CCD coupled to the vertical transfer CCDs, said X-ray emitting means emits X-rays for a period of time less than a frame interval of said solid-state image pickup device,   said storing means includes an offset signal memory which receives offset signal information only when X-rays are not emitted by said X-ray emitting means, and   said subtracting means includes a subtracter for subtracting the output of said offset signal memory from an image signal when X-rays are emitted by said X-ray emitting means, the output of said subtracter being stored in an image memory for subsequent display.   
     
     
       8. A method for offset compensation for use with a solid-state image pickup device, comprising the steps of: producing a plurality of offset signals by said image pickup device when light is not incident on said image pickup device, each offset signal corresponding to a pixel in a frame of pixels;   storing said plurality of offset signals in an offset signal memory;   producing a plurality of image signals by said image pickup device when an optical image is incident on said image pickup device, each image signal corresponding to a pixel in a frame of pixels; and   subtracting each stored offset signal from the corresponding image signal output from said image pickup device to produce a plurality of resulting image signals with accurate offset compensation.   
     
     
       9. The method according to claim 8, wherein said producing plurality of offset signals step and said storing step are continuously repeated until an optical image is incident on said image pickup device. 
     
     
       10. The method according to claim 8, wherein said producing a plurality of offset signals step comprises the substeps of producing a group of offset signals for each pixel and computing an average value for said group, and wherein said storing step comprises the substeps of alternately storing said average value in a first offset memory and storing said average value in a second offset memory   
     
     
       11. An image pickup device comprising: an image pickup camera having its photoelectric surface shielded from external light for producing a frame signal including a plurality of pixels;   means for storing offset signals corresponding to each pixel output from said camera when said photoelectric surface does not receive any light; and   means for subtracting the offset signals stored in said storing means from image signals output from said camera when an optical image of an object falls on the photoelectric surface to produce resulting image signals with accurate offset compensation.   
     
     
       12. The device according to claim 11, wherein said storing means stores offset signals for each frame output from said camera when said photoelectric surface does not receive any light. 
     
     
       13. The device according to claim 11, wherein said storing means comprises: means for calculating an average offset signal for each pixel based upon a plurality of offset signals output from said camera when said photoelectric surface does not receive any light; and   means for storing the most recently calculated average offset signal.